Zack Snyder was the worst thing to happen to the DC films, and I can't say I'm sorry that he wound up sidelined from the "Justice League" after a personal tragedy. His vision of Superman and the other DC superheroes as these heavy, morose, tormented souls was a complete misunderstanding of their appeal, and worse, a bore. There's still a lot of this in "Justice League," and Joss Whedon's contributions to the film often clash terribly with them, but at least the resulting film is watchable, whereas Snyder's "Batman v. Superman" was not.
Let's focus on the good things first. Gal Gadot's Wonder Woman remains a highlight, though she's not given much to do. I also enjoyed Ezra Miller's take on the Flash as a quippy, wet-behind-the-ears newcomer, and Jason Momoa as a shaggy, hard-living Aquaman. Momoa gets one of the movie's best laughs, in a scene involving Wonder Woman's lasso. Frankly, the fact that there are some genuine laughs, and that several of the actors display good rapport with each other, goes a long way toward making up for the rougher, more slapdash parts of the film. I was less impressed by the introductions of Ray Fisher's Cyborg and Amber Heard's Lady Mera, but there's still some potential there.
The movie did nothing, unfortunately, to improve the portrayals of either Batman or Superman. Affleck gamely plays along, but his Bruce Wayne is inert, and his Batman mostly relies on gadgets and vehicles. He seems to be around for exposition more than anything else. I found reports of Henry Cavill's digital mustache removal a little overblown, but he still feels awkwardly shoehorned into the last act of the movie, with nothing resolved about his status as a potential threat to the human race. The film's big crisis, involving the alien invader Steppenwolf, a CGI monstrosity voiced by Ciaran Hinds, is nothing egregiously bad, but it's certainly nothing interesting or enjoyable either.
The action scenes were thankfully comprehensible, in spite of the chaotic plotting that strings them together. Wonder Woman gets a good set piece early on, and and I liked the way the Flash's super-speed was shown in slow-motion. Ironically, it's one of Zack Snyder's little stylistic touches that actually makes sense in context. Aquaman's underwater sequences, however, were pretty poor. I have no idea how they're going to build a feature around this character when they clearly haven't figured out ocean-based action scenes for him yet. Then again, the "Aquaman" movie is being handled by a different director who only has to focus on one hero, so we'll have to wait and see.
I think that the series could continue in this vein for a few more films, and in the right hands it could improve. Joss Whedon, left to his own devices, would probably turn out something a little too close to the "Avengers" movies, but even a knockoff of "Avengers" would be a pretty good outcome considering how rocky the last few DC superhero movies have been. However, as a fan of these characters and this universe, there's a significant part of me that thinks that Warners should just scrap it all and start over from scratch. I expect Superman will need to be rebooted or at least heavily reworked again, as Snyder's just done so much damage to the character.
The upcoming slate of DC movies is totally made up of stand-alone features at the moment, plus the "Wonder Woman" sequel. I sincerely hope the Matt Reeves "Batman" feature can help to course correct the Affleck version of the character a bit, and that a successful "Shazam!" or "Aquaman" might encourage Warners to keep exploring the more obscure DC comics material for a while. "Flashpoint" has been long rumored, and that's the one I'd be the most interested in seeing with the current cast.
However, I don't have much interest in another "Justice League" in the short term, or see much of a future for this version of a shared DC universe. There's been such a stunning mismanagement of the DC IP over the past few years, I'm actually surprised "Justice League" wasn't worse than it ultimately was. I can only hope that the film's failure at the box office will eventually lead to significant changes at Warners, regarding the DC cinematic universe going forward.